Virulence determinants, biofilm production and antimicrobial susceptibility in Staphylococcus aureus causing device-associated infections in a Tunisian hospital.

Staphylococcus aureus is a clinically relevant pathogen that causes device-related infections (DRI) driven by several virulence factors. This study characterized S. aureus isolates involved in DRI in Tunisian patients. Forty consecutive S. aureus strains causing DRI and 47 randomly selected S. aureus strains causing non-device-related infections (NDRI) were collected. All strains were screened phenotypically for antibiotic susceptibility and biofilm forming ability. They were investigated for accessory gene regulator (agr) types, biofilm encoding genes (icaADBC), adhesins, leukotoxins, toxic shock toxin, enterotoxins and exotoxins encoding genes by polymerase chain reaction. Meticillin-resistant S. aureus (MRSA) strains were further characterized by staphylococcal cassette chromosome mec (SCCmec) typing. MRSA rates among DRI and NDRI isolates were 23% and 49% (P=0.02), respectively. The DRI isolates formed biofilm more frequently (n=32) than the NDRI isolates (n=28) (P=0.04), with predominance of the moderate biofilm producer category (P=0.027). All biofilm-positive isolates except four harboured icaADBC genes. A significant difference was observed between DRI and NDRI isolates for fnbA (53-77%), spa (45-26%), sdrD (80-55%) and sen (33-11%) genes. DRI strains were agrI (48%) and agrII (30%) types, whereas NDRI strains were agrI (36%) and agrIII (43%) types. SCCmec type IV was carried by 50% of MRSA isolates. This study highlights the virulence potential displayed by S. aureus isolated from DRI in comparison with NDRI.

Clinical isolates of Pantone-Valentine leucocidin- and gamma-haemolysin-producing Staphylococcus aureus: prevalence and association with clinical infections.

Pantone-Valentine leucocidin (PVL) and gAMMA-haemolysin (Hlg) are members of the synergohymenotropic toxin family produced by Staphylococcus aureus and encoded by pvl and hlg genes, respectively. Many reports describe an association between PVL toxin and necrotic lesions involving skin and mucosa. The aim of this study was to determine the prevalence of S. aureus strains carrying pvl and hlg genes and to investigate a possible relationship between pvl- and hlg-positive S. aureus with specific clinical presentations. Between January 2005 and July 2007, a total of 143 S. aureus strains including 58 meticillin-resistant S. aureus (MRSA) and 85 meticillin-susceptible S. aureus were screened for pvl and hlg genes by multiplex polymerase chain reaction. These strains were isolated from 141 patients for whom demographic and clinical data were recorded. Thirty-one (21.7%) and 77 (53.7%) isolates were positive for pvl and hlg genes, respectively. Twenty-one (67.7%) pvl-positive strains were MRSA (P = 0.001). Among pvl-positive strains, 16 (51.6%) were community-acquired. There was a strong association between pvl genes and skin and soft tissue infections, especially abscesses (60% of strains; P = 0.008) and furunculosis (55.5% of strains; P = 0.036). Our findings confirmed the association between pvl-positive strains, cutaneous infections and meticillin resistance in S. aureus.